DE2652771B2 - Three-chamber electrolysis cell and process for the electrolysis of salts in it - Google Patents

Abstract

PURPOSE:To obtain 30 - 50% caustic alkali with highccurrent efficiency by using an electolysis bath whose cathode, anode and middle rooms are respectively separated by the specified cation exchange membrane. The caustic alkali content in the middle room is controlled to keep the value between 10 and 28%.

Description

R ₁

C-CFR ₂

X for fluorine, chlorine, hydrogen or trifluoromethyl, 'X ₁ for X or CF ₃ (CF ₂ ) ,, where q = 0 or

is an integer from 1 -5, mean.

7. Electrolysis cell according to claim 1 to 6, characterized in that the membrane (B) has a water penetration of 3 g / A · h or less and a hydroxyl ion penetration of 0.4 g / A · h or

ίο has less

8. A method for the electrolysis of salts in three-chamber electrolysis cells according to claim 1 to 7, characterized in that one enters the anode chamber (1) through the inlet (6)

continuously introduces concentrated aqueous alkali halide solution and from outlet (7) a dilute aqueous alkali halide solution continuously withdraws the alkali ions in the intermediate chamber with the alkali ions passing through the Meobran (A) mer (2) formed aqueous alkali metal hydroxide solution adjusts a concentration in the range from! 0 to 20% by weight and in a desired manner Product solution is withdrawn from the outlet on the intermediate chamber (2), which with the through the Membrane (B) through alkali ions in the cathode chamber (3) formed aqueous alkali hydroxide solution ai; f sets a concentration of 30 to 50 wt .-% and this product solution is withdrawn through the outlet (10) from the cathode chamber (3)

9. The method according to claim 8, characterized in that the aqueous hydroxide solution Concentration of 10 to 20% by weight from the intermediate chamber (2) through the connecting pipe (9) introduces into the cathode chamber (3)

10. The method according to claim 8, characterized in that one in the intermediate chamber (2) through the inlet (8) introduces water or dilute aqueous alkali hydroxide solution

SO ₃ H -JCXX ₁ -CFR ₃ ] -

(ü)

wherein

Ri-R? for fluorine or perfluoroalkyl radicals with Ci-Ci ₀ ,

Y for a perfluoroalkyl radical of C ₁ - Cio, / n = 0, 1, 2 or 3, n = 0o'W lp = 0 or 1,

The invention relates to a three-chamber electrolysis cell with an ion exchange membrane as a Dia- phrase and also relates to a process for electrolysis of salts in such pressure chamber electrolysis cells.

It is known; for the electrolysis of aqueous Alkali halide solutions two-chamber electrolysis cells

with selectively permeable ion exchange membranes

w to be used as diaphragms (e.g. DE-OS 19 41 847 and DE-OS 22 51660).

As is known, the membrane arranged between the chambers and in one piece uniformly from a fluorine-containing ion exchange Shear resin exist (DE-OS 22 51 660) or in the form a laminate of fluorine-containing exchange resin and a reinforcing fluorine-free sheet (DE-OS 19 41 847).

Despite the relatively good selectivity of these known

Ion exchange membranes are the electrochemical properties unsatisfactory, because it has has shown that the efficiency of the current is markedly reduced with an increase in the alkali concentration in the cathode chamber. Even if you are very good membranes are used, which have an efficiency of 80% or an alkali concentration in the Deliver cathode chambers of 20% or less, the efficiency often drops to 50% or less.

when the alkali concentration is 30% or higher increases

In order to reduce this disadvantage, multi-chamber electrolysis cells have already become known which have one or more intermediate chambers between the anode and the cathode chamber. One known three-chamber electrolysis cell (US-PS 30 57 794, Fig. 2) contains between the anode chamber and the intermediate chamber made of an ion exchange resin existing diaphragm, and located between the cathode chamber and the intermediate chamber a diaphragm made of asbestos. The electrolysis conditions and process performance for the procedure described there, insofar as the membrane properties are taken into account, exclusively through the exchange membrane between the anode chamber and the intermediate chamber when the intermediate chamber both against the The anode chamber and the cathode chamber is delimited by ion exchange membranes and the difference in alkali hydroxide concentrations between adjacent chambers is kept as small as possible, the otherwise occurring Avoid reducing the current efficiency, but it must correspond to the increased A correspondingly increased voltage is applied to the distance between the electrodes, in particular when if the number of intermediate chambers is increased with the aim of reducing the concentration differences in the To keep chambers as small as possible in order to improve the efficiency.

The invention is based on the object of creating an electrolytic cell that has the lowest possible Number of intermediate chambers brings the greatest possible current yield and one with a high Efficiency working method to create with which an aqueous alkali solution of high concentration in a three-chamber electrolysis cell with an exchange membrane as a diaphragm between the chambers made; len lets

According to the invention, this object is achieved in such a way that between the anode chamber and the intermediate chamber a membrane made of a fluorine-containing ion exchange resin which is resistant to gaseous chlorine and caustic alkali and a thermal efficiency of more than 80%, and Between the intermediate chamber and the cathode chamber, a membrane is used as the main ion exchange residue Exchange resin containing phenolic anchor groups, which is resistant to water Alkali hydroxide solution, a low electrical resistance in aqueous alkali hydroxide solution and a has selective penetration for alkali ions and moderate penetration for water and hydroxyl ions, are arranged, and that in addition to an inlet for saturated saline and an outlet for dilute Saline solution in the anode chamber and an outlet for the product flow at the cathode chamber Intermediate chamber is formed with an outlet for dilute product solution. It can be expedient be that the outlet from the intermediate chamber is designed as a connecting tube leading into the cathode chamber is.

The method according to the invention for the electrolysis of salts in such an electrolysis cell is characterized in that one in the anode chamber through the invitation a concentrated aqueous Continuously introduces alkali halide solution, and from the outlet a dilute aqueous alkali halide solution continuously withdraws the alkali ions passing through the membrane with Jen in the intermediate chamber aqueous alkali metal hydroxide solution formed to a concentration in the range from 10 to 20 Wt .-% adjusts and in the desired manner product solution from that present in the intermediate chamber The outlet withdraws the alkali ions which have passed through the membrane in the cathode chamber

ίο formed aqueous alkali metal hydroxide solution to a concentration adjusts from 30 to 50 wt .-% and this product solution through the at the cathode chamber The existing outlet can be withdrawn if desired.

Introduce a product solution through the connecting pipe into the cathode chamber, and you can do what it may be advantageous to introduce water or a dilute aqueous alkali metal hydroxide solution into the intermediate chamber, for the purpose of setting the desired concentration of the alkali metal present therein: d solution; is to the intermediate chamber expediently with: a separate one Equipped inlet

The invention thus provides for the electrolysis process in a multi-chamber electrolysis cell improve that the alkali metal hydroxide solution formed in the intermediate chamber is separated from the intermediate chamber withdrawn and partially or completely transferred into the cathode chamber and with the therein formed alkali hydroxide solution is mixed.

The invention is explained in more detail below with reference to the drawing, for example. The drawing shows schematically a three-chamber electrolysis cell according to the invention.
This electrolytic cell consists of an anode chamber 1, an intermediate chamber 2 and a cathode chamber 3, which are arranged in series. The anode chamber 1 is separated from the intermediate chamber 2 by the ion exchange membrane A and the intermediate chamber 2 is separated from the cathode chamber 3 by the ion exchange membrane B. An anode 4 is fixedly arranged in the anode chamber 1 and a cathode 5 is fixedly arranged in the cathode chamber 3

Saturated saline solution is supplied to the anode chamber 1 through an inlet 6 and through an outlet 7 diluted solution withdrawn from it.

Water or a dilute alkali solution can be fed into the intermediate chamber 2 through an inlet 8. Through a connecting pipe 9 between the intermediate chamber 2 and the cathode chamber 3 can in the Intermediate chamber formed alkali solution are passed into the cathode chamber. If so desired can not be formed in the intermediate chamber 2 alkali solution directly by one in the drawing outlet shown can be deducted as a product solution.

The concentrated alkali solution located in the cathode chamber 3 is withdrawn as a product through an outlet 10.
Provided that the operating conditions

w> are constant, during the electrolysis the Na + ions formed migrate from the anode chamber 1 in a constant amount through the membrane A into the intermediate chamber 2. Some of these Na ′ ions which enter the intermediate chamber 2 react

M with OH - ions, which migrate to the right of the cathode chamber 3 into the intermediate chamber 2, to form alkali metal hydroxide, while the remaining Na ⁺ ions from the intermediate chamber 2 through the membrane B into the

Kathodimkammer 3 migrate and form alkali hydroxide therein. In this way, all Na + ions that have passed through membrane A are converted to alkali hydroxide.

The alkali hydroxide formed in the intermediate chamber 2 can be drawn off in the form of a dilute solution or instead be transferred through the connecting pipe 9 into the cathode chamber 3.

The current yield of the electrolysis cell is influenced by the migration conditions of the Na + ions through the membrane A and by the alkali concentration in the intermediate chamber 2, which is in contact with the membrane A. but not by the alkali concentration in the cathode chamber 3 and / or the passage values on the membrane B. For this reason, a relatively higher alkali concentration in the intermediate chamber 2 should be avoided. The difference in concentration of the alkali hydroxide solution in the intermediate chamber 2 and the cathode chamber 3 should be kept as large as possible so that an alkali solution which is as highly concentrated as possible can be drawn off as a product solution through the outlet 10.

By adding water and / or alkali hydroxide solution through the inlet 8 into the intermediate chamber 2 and / or withdrawal of product solution from the intermediate chamber 2 through the outlet (not shown) therefrom and / or the connecting pipe 9, the concentration difference regulate in the desired manner.

In the intermediate chamber 2, the alkali hydroxide is converted by reaction of the OH ions that get from the cathode chamber 3 through the membrane B into the intermediate chamber 2, and some of the Na ions that come from the anode chamber 1 through the membrane A into the intermediate chamber 2 arrive, formed. In the cathode chamber 3, the alkali metal hydroxide is formed by the OH ions produced at the cathode and the Na * ions that pass through the membrane B from the intermediate chamber 2 into the cathode chamber 3. Since the membrane is also permeable to water, a certain part of the water passes from the intermediate chamber 2 into the cathode chamber 1. These quantities vary depending on the nature and structure of the membrane.

In order to achieve a 30 percent or higher concentration of alkali hydroxide solution with a current efficiency of 80% or higher, it is advisable to use such an ion exchange membrane B between the intermediate chamber 2 and the cathode chamber 3, which has a water permeability of 3 g / Ah or less and a passage for OH "ions of 0.4 g / A · h or less when the alkali hydroxide concentration in the intermediate chamber 2 is 10-20% by weight and the alkali hydroxide concentration in the cathode chamber 3 is 30-50% by weight. % is held.

It is expedient to use an ion exchanging material with relatively less hydrophilic residues as membrane B. Such residues can be e.g. B. carboxyl, phenol or substituted phenol, mercapto and phosphoric acid residues may be present. Ion exchange membranes which have phenol residues as anchor groups have proven to be particularly favorable: such a membrane shows a superior effect with regard to lower permeability for water and OH ions and lower electrical resistance in the alkaline range.

An example of such a membrane material is a graft copolymer whose main chain has a polyolefin structure with side chains made of hydroxystyrene as the main component, this side chain !! are networked. The graft copolymer can optionally be sulfonated to a certain extent. Such a membrane material containing phenol residues has a comparatively low tendency to swell in relation to water and shows a comparatively low electrical resistance in aqueous alkali solution. A resistor z. B. of 144 ohms / cm ² in a 26 percent aqueous NaCl solution can arise

in only 12 Ohm / cm ² when working in a 20 percent aqueous NaOH solution. Such a property is extremely advantageous because, as in the case of the present invention, the membrane is always used in a caustic alkali solution.

1> The one between the anode and the intermediate chamber Existing ion exchange membranes must be resistant to chemicals, in particular to chlorine and acid in the anode compartment and against caustic alkali predominating in the intermediate compartment.

Furthermore, the membrane must have a current efficiency greater than 80%, preferably more than 85% have an alkali concentration of 10-20% in the intermediate chamber.

As the preferred one suitable for this purpose

2> Membrane material are fluorine-containing synthetic resins to call. For example, polymers or copolymers of at least one of the following can be used Monomers are used: ethylene tetrafluoride, propylene hexafluoride, ethylene trifluoride chloride, ethyl

jo trifluoride, vinylidene fluoride, α-, β-, γ-styrene trifluoride and similar substances. The above-mentioned fluorine-containing monomers can be copolymerized with olefin or olefins such as ethylene and propylene. In this polymer or copolymer can be used as the ionic

Ji exchange-bearing radicals are incorporated z. B. Sulphonic acid, sulfuric acid, carboxylic acid and / or phenol residues, of which a sulfonic acid residue has proven to be particularly beneficial. The one for the The preferred way of introducing these residues is polymerization. As another example of a fluorine Synthetic resin containing a copolymer is to be called, which has a cyclic structure from the structural units (A) and (B) and pendant-type sulfonic acid residues:

R,

C-CFR ₂

(Y),
(R),
SO ₃ H

-4 C XX; - CFR ₃ J-

(A)

Here P. stands for 4O-CRtR ₅ -C Ri- R? for fluorine or perfluoroalkyl radicals

with C-Co,
Y is a perfluoroalkyl radical of

m = 0,1,2 or 3, π = O or i, p = Oor 1, X for fluorine, chlorine, hydrogen or

Trifluoromethyl

Xi for X or CF ₃ (CF ₂ ) ,, where g = 0 or an integer from 1-5.

ion exchange membranes made from a fluorine-containing Resin-made are commercially available.

The ion exchange radicals can be introduced into the fluorine-containing synthetic resin by chemical reaction with the latter. For example, sulfonic acid residues can be introduced into a polymer containing vinylidene fluoride units by chemical reaction therewith. As another example, sulfonic acid residues can be introduced into the benzene rings of a fluorostyrene polymer by a chemical reaction. then to sulfonation, hydrolysis treatment or the like for the introduction are subjected to the lonenaustauschradikale. In particular, the SulfonLrungsprodukte Perfluorstyrols particularly useful for the preparation of membranes for erfindunesgemäße Dreikammprplpjfirrijycpjpjjpn

In an anionic ion exchange membrane from the above-mentioned fluorine-containing synthetic resin, inorganic ion exchangers can be introduced, too which z. B. Zr, Bi, Ti, Ce, Sb, Sn and / or the like belong, so that thereby the solid cathodic ion concentration in the body of the membrane is increased. Such improved membranes can be used in Use for the present purpose to improve the efficiency of the electrical current by 5% or more, compared to those membranes that were left without this treatment or in their commercial condition be used. For the addition of the inorganic exchanger to or for introduction into the interior of the anodic ion exchange membrane, this can be treated with a solution containing z. B. phosphoric acid, Contains tungstic acid, molybdic acid, acid residues of these compounds, their hydroxides and / or oxides, wherein the membrane is covered, immersed or impregnated therein and thereafter in contact with a Solution is brought that contains zirconium ions or vice versa. Jam of this can also, if desired, a Gel product made from zirconium salt including zirconic acid residue, hydroxide residue or the like, in order to coat or impregnate the ion exchange membrane with it.

By using the membrane containing inorganic ion exchangers mentioned above Fluorine-containing synthetic resin can control the range of caustic potash concentration in the intermediate chamber must be maintained to achieve a current efficiency of 80% or higher, is essential be widened. For example, the current efficiency is around 20% when a diaphragm is off fluorine-containing ion exchange resin used that does not contain the above-mentioned inorganic ion exchangers The above-mentioned improvement on the membrane can reduce the caustic alkali concentration to 28% with superior Current efficiency can be increased, with, as desired, at the output caustic alkali of high concentration can be removed.

To further explain the invention, several numerical examples are given below.

example 1

An electrolysis cell was used, divided into three chambers, in which an anode, an intermediate and a cathode chamber were in series and separated from each other by an ion exchange membrane were separated.

As membrane A separating the anode and intermediate chambers, a membrane was used which is mentioned below as membrane No. 1 and which was a laminate of fluorine-containing ion exchange resin and a screen sheet of ethylene tetrafluoride resin.

As the second membrane B separating the intermediate and cathode chambers, one became commercially available

ίο available ion exchange membrane used that here is mentioned as membrane no. 2 and carried phenol residues or their derivatives.

Then, a hydrolysis treatment of a NaCl aqueous solution was carried out in the following manner

Ii executed:

Aqueous saturated NaCl solution was fed into the anode chamber and water was fed into the intermediate chamber. The total amount of aqueous NaOH solution contained in the Z'A'ischcr.karrirricr in the% 'crlauf des

2n process arose, was transferred from this via an overflow connection into the cathode chamber, the highly concentrated NaOH solution of which was withdrawn from the cathode chamber.
The results are given in Table 1 below.

The extent of the water and OH penetration at the ion exchange membrane B was measured after the overflow pipe 9 had been removed. For this purpose, an aqueous NaCL solution was placed in the anode chamber.

solution of constant concentration and in the intermediate and the cathode chamber in each case an aqueous NaOH solution with correspondingly constant concentrations fed in. These conditions were adjusted so that the resulting aqueous product

j5 NaOH solutions from the intermediate and cathode chambers Had concentrations of about 19% and 39%, respectively. The corresponding water contents were then determined the NaOH solution supplied to the cathode chamber and the NaOH solution withdrawn from it via a certain Period of time together with the corresponding water consumption by the hydrolysis and by The amount of water passing through the two membranes was measured, the corresponding electrical Power consumption on the membranes was determined.

The amount of NaOH formed in the intermediate chamber was calculated on the basis of the measured amounts and concentrations of the NaOH supplied to and discharged from the intermediate chamber. The amount of OH ions consumed to form NaOH was also calculated. Furthermore, the amount of OH "ions which were transferred into the ancdene chamber was calculated on the basis of the current efficiencies which were calculated from the amounts of MaOH in the intermediate and cathode chambers the amount of OH ~ taken, which had been transferred from the cathode chamber into the intermediate chamber through the second membrane B.

Table 1

anode Titanium / ruthenium oxide cathode Steel wire mesh Brine 26% aqueous NaCL solution Bath temperature SO ⁰ C Current density 20 A / dm? Bad tension 4.0V

continuation

NaOH concentration in the

Intermediate chamber 19%

NaOH concentration in the

Cathode Chamber 39%

Current efficiency 82%

Flow of aqueous

NaOH through the

Connecting tube 2.09 g / Ah in

Water flow rate

through membrane # 2 1.34 g / A · h

OH - amount of penetration through

Membrane No. 2 0.29 g / A · h

Example 2

A membrane made of fluorine-containing ion exchange resin was compressed into a 10% solution of ZrOC! "· 2 HO ir!! Ν. HC! Z'.vsi S'.undsn! Ars""and then taken out. The membrane surfaces were covered with filter paper wiped off. Then, the membrane the first membrane a, below was one hour immersed in a 85% H3PO4-LO-sung immersed, washed with fresh water and dried in a dryer for one hour at 160 ⁰ C. mentioned as membrane no. 3, The second membrane B was the same membrane as used in Example 1 and was used as a partition between the cathode and intermediate chambers. The other electrolytic conditions were the same as in Example 1 for the production of NaOH from NaCl. The results are given in Table 2.

The permeation rates of water and OH- on the membranes were determined in the same manner as in Example 1 certainly.

Table 2

anode

cathode

Bath temperature

Current density

Bad tension

NaOH concentration in the

Intermediate chamber

NaOH concentration in the

Cathode chamber

Current efficiency

Flow of aqueous

NaOH through the

Connecting pipe

Water flow rate

of membrane no. 2

OH - penetration rate

Jer membrane No. 2

The results are shown in Table 3. The leaking amounts of water and OH- were determined in the manner explained above.

Table 3

Titanium / ruthenium oxide

Steel wire mesh

26% aqueous

NaCL solution

8O ⁰ C

20 A / dm ²

4.2V

25%

44%

85% so

2.09 g / A · h

1.40g / Ah

0.27 g / A · h

Example 3

As first membrane A, a laminated membrane was used, here called membrane Nos. 4 and fluorine-containing ion exchange resin and a mesh sheet made of Athylentetrafluoridharz contained as a second membrane B, separating the intermediate and cathode chambers, the same membrane # was. 2 as used in example i. The other electrolytic conditions were the same as described above for the treatment of NaCl.

anode Example Titanium / ruthenium oxide cathode Steel wire mesh Brine 26% aqueous NaCI solution Bath temperature 8O ⁰ C Current density 20 A / dm ² Bath voltage 3.8V NaOH concentration in the intermediate chamber 12% NaOH concentration in the cathode chamber 31% Current efficiency 87% Flow of aqueous NaOH through the Connecting pipe 2.17 g / A · h Water flow rate on membrane No. 2 1.45 g / A · h OH- penetration rate of membrane no. 2 0.26 g / A · h el 4

20th

25 as a membrane A membrane was No. 4 according to Example 3 was used. Membrane No. 2 from Example 1 was used as membrane B. An aqueous NaCl solution was electrolyzed, with water being fed into the intermediate chamber. Fairly dilute NaOH solution and fairly concentrated NaOH solution were withdrawn from the intermediate and cathode chambers, respectively. The results are given in Table 4.

Table 4

anode

cathode

Brine

Titanium / ruthenium oxide

Steel wire mesh

26% aqueous

NaCI solution

8O ⁰ C

20 A / dm *

3.8V

Bath temperature

Current density

Bath voltage

NaOH concentration in

of the intermediate chamber 10%

NaOH concentration in

the cathode chamber 45%

Current efficiency 90%

From the cathode chamber

Amount of NaOH taken 0.806 g / A · h

From the intermediate chamber

Amount of NaOH removed 0.537 g / A · h

Water flow rate

on membrane # 4 2.11 g / A · h

Water flow rate

on membrane No. 2 1.66 g / A-h

OH - penetration rate

on membrane No. 2

0.29 g / A · h
Comparative example

It was the same as the first and second Memhran

A and B membranes made of the same fluorine-containing ion exchange resin were used. The other electrolysis conditions were the same as in Example 1.

The cathode chamber became an aqueous 30% NaOH solution and the intermediate chamber an aqueous one 10% NaOH solution supplied The water supply

to the intermediate chamber and the flow conditions are adjusted so that the alkali concentration in the cathode chamber was 30% and the electric current efficiency was more than 80%. The initial voltage was 5.0 V; after one hour, counting from the beginning of the electrolysis, the applied voltage gradually increased. It was determined, that gases collected in the connecting pipe 9 which connected the intermediate and cathode chambers. at As the voltage increased further, the temperature in the intermediate chamber rose suddenly and noticeably until the

Bath liquid / u began to boil. Further continuation of the electrolysis became impossible under these operating conditions.

The permeation rates of water and OH- were determined on the membrane B in the same manner as described above, and were 3.53 g / A · h and 0.21 g / A · h, respectively.

From these results it could be concluded that the second membrane used according to the invention Membrane carrying phenol radicals is more suitable for the purpose described.

For this purpose I sheet drawings

Claims (6)

Patent claims: 1. Three-chamber electrolysis cell with ion exchange membrane as a diaphragm, characterized in that between the anode chamber (1) and the intermediate chamber (2) a membrane (A) made of a fluorine-containing ion exchange resin, which is resistant to gaseous chlorine and caustic alkali and a current efficiency of more than 80%, and between the intermediate chamber (2) and the cathode chamber (3) a membrane (B) made of exchange resin containing phenolic anchor groups as the main ion exchange residues, which is resistant to aqueous alkali hydroxide solution, low electrical resistance in aqueous alkali hydroxide solution and selective penetration for Al ^ aliionen as well as a has moderate penetration for water and hydroxyl ions, and that in addition to inlet (S) for saturated saline and Outlet (7) for dilute saline solution in the anode chamber (1) and outlet (10) for the Product flow to the cathode chamber (3), the intermediate chamber (2) is formed with an outlet for dilute product solution 2. Electrolysis cell according to claim 1, characterized in that the outlet from the intermediate chamber (? ^{X is designed} as a connecting pipe (9) leading into the cathode chamber (3). 3. Electrolytic cell according to claim 1 or 2, characterized in that the intermediate chamber (2) is designed with an inlet (8) for water or dilute alkyl hydroxide solution. 4. Electrolysis cell according to claim 1 to 3, characterized in that the membrane (A) contains inorganic ion exchangers in addition to the fluorine-containing ion exchange resin 5. Electrolysis cell according to claim 1 to 4, characterized in that the ion exchange resin of the membrane (A) contains sulfonic acid residues as the main anchor groups. 6. Electrolysis cell according to claim 1 to 5, characterized in that the membrane (A) contains an ion exchange resin cyclic structure from the following structural units (i) and (ii):